1. Field of the Invention
The present invention relates to an apparatus for gripping nano-size objects, and more particularly to a gripping apparatus which utilizes electrostatically-driven carbon nanotubes for gripping nano-size objects.
2. Description of the Prior Art
The development of new tools for manipulating and probing matter at a nanometer length scale is critical to advances in nanomechanics, nanoscale physics, and nanotechnology. Atomic force microscopes, scanning probe microscopes and scanning tunneling microscopes are currently used for these purposes because these microscopes are capable of working at length scales as small as a single atom. However, conventional atomic force microscopes, scanning probe microscopes and scanning tunneling microscopes are provided with a single probe tip which limits the ability to manipulate nano-objects. That is, the single probe tip cannot grab an object and, therefore, cannot provide for secure and accurate movement of the nano-object to a desired destination or position.
Nanotweezers have been developed to grip and manipulate nano-objects in view of the limitations of the above-mentioned microscopes having the single probe tip. The nanotweezers can grip and release objects, thereby facilitating new kinds of operations and assembly of nano-scale particles and structures.
For example, as shown in FIG. 1, a pair of nanotweezers 88, developed Phillip Kim and Charles M. Lieber (“Nanotube Nanotweezers”, Journal of Science, volume 286, pp. 2148-2150, Dec. 10, 1999), includes metal electrode films 84a and 84b which are respectively formed on circumferential surfaces of a tapered glass tube 80 with an insulating section 82 interposed therebetween. Carbon nanotubes 86a and 86b are respectively fastened to the metal electrode films 84a and 84b so that the carbon nanotubes 86a and 86b protrude to form the nanotweezers 88.
As shown in FIG. 2, when a voltage is applied from a direct-current power supply 94 to the nanotweezers 88 via lead wires 92a and 92b connected to contact points 90a and 90b on the metal electrode films 84a and 84b, the carbon nanotube 86a is charged to a positive polarity, while the carbon nanotube 86b is charged to a negative polarity. As a result of the electrostatic attractive force of these positive and negative charges, the tip ends of the carbon nanotubes 86a and 86b close inward, so that a nano-substance 96 can be gripped between the tip ends. If the voltage is reduced to zero, the electrostatic attractive force is eliminated, so that the carbon nanotubes 86a and 86b are caused to return to the state shown in FIG. 1 by the elastic recovery force of the carbon nanotubes 86a and 86b and the nano-substance 96 is thereby released. Thus, opening-and-closing control of the nanotweezers 88 can be accomplished by controlling the magnitude of the voltage, e.g., 0 to 10 V, applied to the metal electrode films 84a and 84b. 
However, the nanotweezers 88 have several drawbacks. More specifically, a first drawback is that since the tip ends of the glass tubes 80 are finely worked to 100 nm in a tapered form, the nanotweezers 88 are relatively weak and brittle.
A second drawback results from the metal electrode films 84a and 84b being formed along the entire length of the glass tube 80, and the contact points 90a and 90b being disposed on the large-diameter rear portion of the glass tube and connected to the power supply 94 via the lead wires 92a and 92b. In particular, since the lead wires 92a and 92b have a considerable thickness, the electrical contact points 90a and 90b must be disposed on the rear end portion of the glass tube which has an expanded diameter. This results in the difficulty of forming the metal electrode films along the entire length of the glass tube and in poor efficiency.
A third drawback arises from the fact that the nanotweezers are operated by electrostatic action between the carbon nanotubes 86a and 86b. That is, positive and negative electrical charges are accumulated in the carbon nanotubes 86a and 86b, and the opening and closing of the carbon nanotubes 86a and 86b is controlled by the electrostatic attractive force of these electrical charges. In the case where the nano-substance 96 is an electrical insulator or a semiconductor, such an electrostatic attractive force can be effectively utilized. However, in the case where the nano-substance 96 is a conductor, the ends of the carbon nanotubes 86a and 86b are electrically short-circuited, so that the electrostatic attractive force ceases to operate. Furthermore, there is also a danger that the nano-substance 96 will be electrically destroyed in the case of short-circuiting. Accordingly, the use of the nanotweezers 88 is limited to semiconductor nano-substances and insulating nano-substances, and constant care must be taken during use.
A fourth drawback is that-since the nanotweezers 88 are constructed from only two carbon nanotubes, there are various shaped nano-substances that cannot be securely gripped. For example, although flattened nano-substances can be stably gripped by the two carbon nanotubes 86a and 86b, the gripping hold on a spherical nano-substance or rod-like nano-substance may be unstable such that there is a risk that the nano-substance will fall out of the nanotweezers.
With reference to FIG. 3, U.S. Pat. No. 6,669,256 to Nakayama et al. discloses nanotweezers 50 including three nanotubes 54 whose base end portions are fastened to a holder 51 such that the nanotubes protrude from the holder 51. The nanotubes 54 are coated with a coating film which insulates and covers the surfaces of the nanotubes 54. Lead wires 52 are connected to the nanotubes 54 via electrode films 53. The tip ends of the nanotubes 54 are freely opened and closed by means of an electrostatic attractive force generated by applying a voltage across the lead wires 52 such that two of the nanotubes 54 are negatively charged while the third nanotube 54 is positively charged.
The coating film on the nanotubes 54 is made of an insulative material in order to prevent short-circuiting between the nanotubes 54 and a nanosubstance to be gripped. For example, the coating film may be a hydrocarbon film formed on the surfaces of the conductive nanotubes by electron beam irradiation. However, the method for forming the coating film is quite complicated in case of nano-scale objects such as carbon nanotubes. Further, the thickness of the carbon nanotube shell is equal to one carbon atomic layer. Hence, the layer of any new material can be expected to sufficiently change the electrical and mechanical properties of the carbon nanotubes.
Even though the nanotubes are covered with the insulative coating layer, the risk of short-circuiting still exists in the case where a higher voltage is applied, accidentally or intentionally to generate a stronger attractive force, or in the case of a defect (cracking, thinning, breakage, etc.) of the coating film, e.g., due to material fatigue. The likelihood of a defect occurring in the coating film is increased as the coating film covering the nanotubes is repeatedly exposed to large deformations, and hence, very strong stresses originate in the material causing cracks and film destruction.
Further, despite the insulative coating film, an electro-magnetic field exists between charged nanotubes which can adversely effect some types of objects in an harmful and unpredictable manner, especially biological living substances such as cells, genes, DNA, etc.
Lastly, while the use three or more nanotube arms provides for more secure gripping of a nanosubstance, this results in complex interaction among the positively and negatively charged nanotubes.